Disinfecting solutions for the care of contact lenses are well known in the art and the use of such lenses and solutions often involves a daily disinfecting regimen. The present market of lens care solutions includes multipurpose solutions, which include one or more antimicrobial components, and solutions that include about 3 wt. % hydrogen peroxide. One apparent advantage of a hydrogen peroxide lens care disinfecting system is the absence of a disinfecting agent in the solution or the lens following neutralization of the hydrogen peroxide with the exception of residual amounts of hydrogen peroxide, generally less than 100 ppm.
In general, the hydrogen peroxide systems include a disinfecting solution that contains hydrogen peroxide into which previously worn contact lenses are placed and allowed to remain in contact with the solution for a specified period of time. The hydrogen peroxide is believed to (1) oxidize chloride in the bacteria to hypochlorite or (2) decompose into nascent oxygen and hydroxyl radicals, thus providing an antimicrobial effect. Following or simultaneous with this disinfection cycle the peroxide solution requires neutralization, and this can be carried out either by catalytic reduction with a supported platinum catalyst or with an enzyme such as catalase. Following neutralization the contact lens may be reinserted into the eye without a separate rinse step as the hydrogen peroxide has been neutralized to levels that are non-irritating to ocular tissues.
Consumer friendly, single step peroxide disinfection systems have achieved near exclusive popularity, e.g., the AO Sept system by Ciba Vision and the EZ Sept system by Bausch & Lomb. These two systems operate by placing a contact lens to be disinfected in contact with a solution of peroxide and a platinum disk whereby peroxide disinfection and peroxide neutralization occur essentially simultaneously. The user places the lenses in the lens holding compartments, adds the disinfecting solution to the system container, closes the container placing the lenses in contact with the solution and waits the appropriate time interval, typically four to eight hours, before removing the lenses from the disinfection system. The lenses can then be directly inserted onto the eye.
In hydrogen peroxide systems that rely upon a platinum catalyst, the hydrogen peroxide in solution is neutralized relatively quite rapidly. Consequently, lens disinfection at the higher peroxide concentrations is somewhat limited in time. For example, in an AO Sept system in which the initial concentration of hydrogen peroxide is 3%, it is said that the concentration of the hydrogen peroxide falls rapidly to about 0.1% in about 12.5 minutes. See, U.S. Pat. No. 5,306,352. After this point, the neutralization of the remaining hydrogen peroxide proceeds relatively slowly and it takes several hours, i.e. up to 8 hours or more, before the hydrogen peroxide is depleted sufficiently so that the contact lens can be inserted onto the eye without fear of irritation or injury.
U.S. Pat. No. 5,306,352 to Nicolson et al. recognizes the need to control the catalytic decomposition or neutralization reaction of the hydrogen peroxide such that concentration of the hydrogen peroxide remains at higher levels during the initial stages of neutralization, yet maintain the necessary degree of neutralization to allow for direct insertion of the disinfected lens onto the eye without the need for rinsing the lenses. In FIG. 1 the hydrogen peroxide neutralization rate of the AO Sept system is plotted in which a platinum catalyst is contacted with a 3% hydrogen peroxide solution. In such situation, it is noted that the concentration of the hydrogen peroxide falls rapidly to about 0.1% in about 12 minutes. FIG. 2 represents a decomposition profile of a hydrogen peroxide system in which the rate of decomposition of the hydrogen peroxide is said to be controlled by means described by Nicolson.
Nicolson lists five general steps one could consider in the catalytic decomposition of hydrogen peroxide: (1) the transportation of the hydrogen peroxide to the catalyst to insure a continuous contact between the catalyst and hydrogen peroxide; (2) the absorption of hydrogen peroxide to the catalyst surface; (3) the neutralization or catalysis in which the hydrogen peroxide is decomposed to water and nascent oxygen; (4) the desorption from the surface of the reaction products, i.e. the water and nascent oxygen, or other contaminants so as to expose the active sites; and (5) the transportation of the reaction products away from the catalytic surface. Nicolson does not, however, clearly describe how one of skill might actually control any one of these reaction (neutralization) stages to achieve a desired neutralization curve.
With respect to step (3), Nicolson proposes that the catalyst be partially poisoned in the manufacturing setting prior to sale and first use by the consumer. To determine whether the catalyst is sufficiently pre-poisoned, the generation of oxygen from the system can be measured. As stated, in a typical AO Sept system using platinum as a catalyst one can estimate the rate of neutralization from the initial generation of oxygen at about 40 mL/min. Nicolson proposes that the catalyst be sufficiently pre-poisoned so that the amount of oxygen liberated during the reaction is periodically measured until the oxygen liberation rate is somewhere between 2 and 15 mL/min, and preferably between 2 and 5 mL/min. Again, there is no description in Nicolson as to how one might pre-poison a platinum catalyst to achieve the proposed peroxide neutralization rate.
Instead, Nicolson focuses on a mechanical/chemical means referred to as a “buoyance mediated control system” to delay hydrogen peroxide neutralization in contact lens disinfecting systems. It is stated that the absorption of generated oxygen gas provides a neutralizing catalytic particle sufficient buoyancy to rise to the surface of the peroxide solution. Buoyancy controlled catalytic reactions fall into two primary types of reactions. First are those reactions which generate a gas. The gas bubbles adhere to the surface of the catalyst particle creating a buoyant particle. The buoyant particle rises to the surface where the gas bubble escapes to the gas phase over the liquid reaction medium. Upon losing the gas bubbles, the catalyst loses buoyance and begins to descent until it again contacts liquid containing reactants so that further buoyant gas bubbles can be generated. This bobbing action is, therefore, confined to the uppermost layers of the solution leaving the lower portion of the solution in a relatively non-neutralized state for a greater period of time. One perceived problem with the floating particle method is preventing the particles from adhering to the lenses, and thereby, avoiding the need for a separate rinse solution.
In the second type of buoyancy controlled catalytic reaction, the catalytic particle resides at or near top of the solution due to its density. If the reaction product solution is less dense than the reactant solution, then the reaction proceeds substantially from top to bottom and the catalytic particles are designed to be slightly less dense than the reactant solution (i.e. between the reaction product and reactant solution densities). If the reaction product solution is more dense than the reactant solution, then the reaction proceeds from bottom to top and the catalytic particle is designed to be slightly more dense than the reactant solution. In either event, the catalytic particle must return to contact the reactant solution if the neutralization reaction is to proceed. In either case, these buoyancy controlled processes are very complex and impose substantial limitations on commercial viability or applications.
The presently marketed peroxide disinfection systems have been around for over twenty-five years with little or no improvement in disinfection profile. Surfactants have been added to assist in protein and lipid cleaning, but little, if any, progress has been made to improve upon the biocidal effectiveness of lens care peroxide systems. Neither have there been any advances in a peroxide disinfectant system that makes it possible to control the neutralization rate of the hydrogen peroxide. There is a need to address these drawbacks in the currently marketed lens care peroxide systems, and to improve upon the disinfection and effective storage of the lenses after complete neutralization of the hydrogen peroxide.